The present invention relates to a method of adjusting a thermal balance of rotor for a rotary electric machine and, more particularly, to a rotor thermal-balance adjusting method in which the rotor is provided with a coolant passageway. Coolant such as, for example, hydrogen is passes through the coolant passageway to cool the rotor.
In general, balance adjustment is applied to a rotary element to reduce shaft-vibration as much as possible. One method of balance adjustment of the rotary element uses a balance weight which is adjusted in magnitude and position to adjust the balance of the rotary element. This adjusting method is relatively simple, and can balance the rotary element with a high degree of accuracy.
In the case of a rotor for a rotary electric machine, however, the rotor itself is charged with heat so deflections of the rotor shaft due to the heat occur, as well as local shaft-deformation due to non-uniformity in heat radiation from the rotor surface. That is, shaft-deformation due to a thermal imbalance, resulting in shaft-vibration. It is impossible for mere mechanical or formal balancing to reduce the shaft-vibration.
It is extremely difficult to eliminate the thermal imbalance. Research has been conducted to avoid the thermal imbalance, and various thermal-balance adjusting methods have been proposed. However, a satisfactory method has not yet been proposed.
Of the conventional methods, a relatively excellent thermal-balance adjusting method is known from, for example, Japanese Patent Publication No. 58-40899. In the method proposed in the Japanese patent, a cooling-medium flow passageway within the rotor is regulated to eliminate the thermal imbalance. It is possible for this method to effect a superior thermal balance, if it is clear which main component is to be corrected. It is a problem, however, that the superiority depends on how the component to be corrected should be accurately detected or calculated.
It will suffice for a general rotary electric machine to have the rotor driven both under no load condition and under an actual load condition. A shaft-vibration component of the thermal imbalance is detected, and a corresponding correction is made to the shaft-vibration component of the thermal imbalance. Accordingly, it is possible for the general rotary electric machine to effect the thermal balance without any difficult. It is usual for a rotary electric machine which is large in capacity, however, to have, in spite of the balance adjustment being sufficiently been carried out, thermal imbalance which is not sufficiently eliminated. The reason for this is that, since the balance adjustment is carried out within a factory under a stimulated load, and since some of the rotary electric machines employ, as cooling medium, special gas such as, for example, hydrogen gas, the cooling condition due to the coolant at adjustment of the thermal balance differs from that at practical running. That is, even in the rotary electric machine of the kind referred to above which employs the hydrogen gas as the coolant, the hydrogen gas may not be used for balance adjustment because of explosive danger. It is usual for such a rotary electric machine to carry out the balance adjustment using, in general, cooling air as the coolant. For this reason, even if the rotor itself is the same temperature as the actual load condition, flow rate of the coolant at each section and cooling performance at the balance adjustment differ from those during actual running because hydrogen gas and air perform differently as the coolant. Accordingly, even if the thermal balance is excellent at the balance adjustment within the factory, the thermal balance is not necessarily excellent under the practical-use load condition.